öpcaö variable refrenced before assignment

[markotaht at gmail.com]

fail4 = "palgad.txt"

f4 = open(fail4, "r")

def koguarv_ridu failis(f):
    for i, l in enumerate(f):
        pass
    return i+1

def palgad(f4):
    palgad = 0
    while True:
        f4r = f4.readline()
        if f4r == "":
            break
        palgad += int(f4r[f4r.find(";")+1:])
    return palgad

def kuu_keskmine(palgad, f):
    return palgad/koguarv_ridu_failis(f)

print(kuu_keskmine(palgad(f4), f4))


Why does it give me local variable "i" referenced before assignment in koguarv_ridu_failis(f) on the return i+1 line
But if i do directly koguarv_ridu_failis(f4) then i get correct antswer.